Earliest chess engines that have features of AB pruning?

[Nay Lin Tun]

I wanna know some evidence as I had an argument with someone!
My assumption was approximately 15 years ago, may be in crafty by Robert Hyatt.
I also think that early engines like the king (chess master 6000) did not have AB pruning!

[chrisw]

I wanna know some evidence as I had an argument with someone!
My assumption was approximately 15 years ago, may be in crafty by Robert Hyatt.
I also think that early engines like the king (chess master 6000) did not have AB pruning!

For chess engines using microprocessors since about 1980, all except those written in BASIC which were evaluation function only and no search, used alpha-beta, as far as I know. It didn’t take much to realise that a full alpha search (minimax only) effectively evaluated and ranked all the root moves and for playing chess it was only necessary to know the “best” move, ranking all the others in order being redundant information. AB is the algorithm that performs the redundancy elimination.

[Joost Buijs]

My first chess engine that I wrote back in 1977 was already using a-b pruning, at that time it was nothing new, I think the algorithm was already known 15 years earlier, but it became widespread around 1975.

[Rom77]

NSS (1958), https://www.chessprogramming.org/NSS

The final choice depends on an acceptance value and if a move receives a value greater than this threshold it is played, otherwise the best move found by the alpha-beta backing up procedure will be made.

[Nay Lin Tun]

Ok, thanks.
It was much earlier than I know.
I thought AB pruning was popular only after deep blue.

[hgm]

Alpha-beta pruning was already described in elementary textbooks for AI courses when I was a math student in 1976.

BTW, human chess players have used it far before computers could play chess, even though they don't know it. If you ask a chess player that has been thinking about a position why he is not worried about a particular line that would be cut off by alpha-beta, and he will look at you like you are crazy. Chess players know very well that a single refutation of a move is enough, and don't continue looking for more or better refutations when they find one.